Multivitamins typically contain a large number of vitamins and minerals. Some of the ingredients can be harmful when taken in large amounts. For example, oil-soluble vitamins such as vitamin A or potentially toxic minerals such as selenium that are typically contained in multivitamins can be toxic at high doses. The potential toxicity of some of the components in multivitamins prevents a user of multivitamins from taking high enough multiples of daily multivitamins to receive any reduction in blood pressure that high doses of the components that modulate blood pressure might bestow. Also, multivitamins aren't formulated based on the capacity of the various ingredients to reduce blood pressure, and are lacking in ingredients known to reduce blood pressure but not categorized as essential vitamins and minerals.
Multisupplements that are not formulated for blood pressure reduction have similar shortcomings. Components that do not reduce blood pressure but are present in amounts that constitute a high percentage of a tolerable dose limit the total number of the multi-supplement tablets or capsules that can be safely taken in a day.